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An entry-level understanding of the CSS knowledge system

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Jul 09, 2021 pm 01:50 PM

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Let me share the CSS system diagram. It is very useful. Please save it. The following article will introduce you to the introductory knowledge of CSS.

An entry-level understanding of the CSS knowledge system

CSS system

css You can have a rough understanding of the following:

An entry-level understanding of the CSS knowledge system

CSS3

##Cascading Style SheetCascading Cascading Style SheetFont , color, margin, height, width, background image, web page positioning, web page floating...css selector (emphasis)Beautify the web page (text, shadow, hyperlink, list, gradient )Box modelFloating, positioningWeb page animationAdvantages of css;1. Separation of content and performance2. The web page structure is unified and can be reused3. The styles are very rich4. It is recommended to use css files independent of html5 , Use SEO to easily be included by search engines!

1. Selector

1. Select a certain item on the page One or a certain type of element

Tag selector
Class selector
id selector
Level selector
Descendant selector: After an element

body p{
      background: #c56b22;
  }

2. Sub-selector

/*子选择器，只选择向下一代*/
body>p{
      background: deepskyblue;
  }

3. Adjacent sibling selector

/*相邻兄弟选择器，只有一个，向下*/
  .active + p{
      background: orange;
  }

4.Universal selector

/*通用兄弟选择器，当前选中元素的向下的所有元素*/
  .active~p{
      background: aquamarine;
  }

2. Pseudo-class selector

/*ul的第一个子元素*/
ul li:first-child{
    background: #c56b22;
}
/*ul的最后一个子元素*/
ul li:last-child{
    background: aqua;
}

/*选中p1,定位到父元素，选择当前的第一个元素
选择当前p元素的符集元素，选择符父级素的第一个，并且是当前元素才生效
*/
p:nth-child(1){
    background: antiquewhite;
}
/*选中父元素，下的p元素的第二个，按类型*/
p:nth-of-type(2) {
    background: #b04a6f;
        }

3. Beautify the web page

1. Font style

<!--
font-family:字体
font-size:字体大小  px代表像素，em代表一个字的缩进大小
font-weight:字体粗细 最大800，相当于bolder
color:字体颜色
-->
<style>
    body{
        font-family: Arial;
    }
    h1{
        font-size: 40px;
    }
    p[class=p1]{
        font-weight: bold;
        color: #b04a6f;
    }
</style>


<style>
    /*字体风格*/
    /*斜体 加粗 大小 字体*/
    p{
        font:oblique bold 20px Arial;
    }
</style>

2. Text style

color rgb rgba
text-align=center
text-indent:2em
line-height:Single line text is centered up and down!
text-decoration:
/middle is vertical /vertical-align: middle;

3. Shadow

<style>
    #price{
        /*阴影颜色，水平偏移，垂直偏移，垂直半径*/
        text-shadow: #c5527d 5px -5px 1px;
    }
</style>

<body>
<p id="price">
    ¥30
</p>
</body>

4. Hyperlink pseudo-class

<style>
    /*默认的颜色*/
    a{
        text-decoration: none;
        color: #000000;
    }
    /*鼠标悬浮的颜色*/
    a:hover{
        color: #c56b22;
        font-size: 20px;
    }
    /*鼠标按住的颜色*/
    a:active{
        color: #c5527d;
    }
    /*鼠标未点击链接的颜色*/
    /*a:link{*/
    /*    color: gray;*/
    /*}*/
    /*!*链接已访问状态*!*/
    /*a:visited{*/
    /*    color: #66ccff;*/
    /*}*/
</style>

<body>
<a href="#">
    <img src="/static/imghwm/default1.png"  data-src="images/1.jpg"  class="lazy"   alt="图片加载失败">
</a>
<p>
    <a href="#">《从0到1开启商业与未来的秘密》</a>
</p>
<p>
    作者：[美]<a href="#"> 彼得·蒂尔，布莱克·马斯特斯（Blake Masters）</a>著，
    <a href="#">高玉芳</a> 译
</p>
</body>

5, List

1) Background

Background color
Background image

<style>
    div{
        width: 800px;
        height: 500px;
        border: 1px solid #fcb4dc;
        /*默认全部平铺*/
        background-image: url("image/1.jpg");
    }
    .div1{
        background-repeat: repeat-x;
    }
    .div2{
        background-repeat: repeat-y;
    }
    .div3{
        background-repeat: no-repeat;
    }
</style>

.title{
    font-size: 18px;
    /*font: oblique bold 20px/30px Arial;*/
    font-weight: bold;
    text-indent: 1em;
    line-height: 35px;
    /*background: #fcb4dc;*/
    /*颜色、图片、位置、平铺方式*/
    background: #fcb4dc url("../image/d.jpeg") 250px 4px no-repeat;
}

ul li{
    /*行高*/
    height: 30px;
    list-style: none;
    text-indent: 1em;
    /*background: url("../image/r.jpeg") 200px 1px no-repeat;*/
    background-image: url("../image/r.jpeg");
    background-repeat: no-repeat;
    background-position: 200px 1px;
}

2) Gradient

background-color: #A9C9FF;
background-image: linear-gradient(60deg, #A9C9FF 0%, #FFBBEC 100%);

3) Box model

Border
Inner and outer margin
Rounded border
Floating

4) Parent border collapse problem

/*
clear:right;    右侧不允许又浮动元素
clear:lerf;     左侧不允许有浮动元素
clear:both;     两侧不允许有浮动元素
clear:none;
*/

Solution: Increase the height of the parent element

#father{
 border:1px #000 solid;
 height:800px}

Add an empty p tag and clear the floating
```

```

.clear{
    clear:both;
    margin:0;
    padding:0;}

overflow

#在父级元素中添加一个 overflow:hodden;

Add a pseudo-class

#father:after{
 content:'';
 display:block;
 clear:both;}

to the parent class

If it floats, it will break away from the standard document flow, so we need to solve the problem of parent border collapse

6. Positioning

Specify offset relative to the original position, relative positioning If so, it will still be in the standard document flow! The original position will be retained
position:relative
```
top:-20px;
left:20px;
bottom:-10px;
right:20px;
```

position:absolute

定位:基于xxx定位，.上下左右~
1、没有父级元素定位的前提下，相对于浏览器定位
2、假设父级元素存在定位,我们通常会相对于父级元素进行偏移~
3、在父级元素范围内移动
相对于父级或浏览器的位置，进行指定的偏移,绝对定位的话，它不在标准文档流中，原来的位置不会被保留

position:fixed

Level, the default is 0, the highest is unlimited

/*背景透明度,或者使用rgba，早期版本filter:alpha(opacity=50)*/
opacity:0.5
/*filter:alpha(opacity=50)*/

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